What's selection bias?

  • Selection on IV
  • Selection on DV

Ideal situation

Different types of selections

Selection on IV

Selection on DV

Selection on Both

The consequence of selection bias

  • When your case study suffers from selection bias,

  • Any characteristics that the selected cases share is a cause.
  • The relations between variables within the selected set reflect a general pattern.

Example

  • Question: Why new industrializing countries (NICs) grows more rapidly?
  • Theory: The repression of labor

  • Case:

  • What type of design this is?

What's the problem?

When selection is not a problem

  • Theory-oriented
    • Labor repression contributes to growth in a at least mixed economy
    • Case selection: Communist countries are excluded.
  • Hypothesis-oriented
    • Theory: Military governments are more likely to negotiate their extrication from power than are personalist regimes.
    • Hypothesis: Incidence of negotiation in military governments during the years in which breakdown occurs is higher than that in personalist regimes.
    • Case selection: Only breakdown regimes are select.

Avoid selection bias (when it's possible)

  • Being clear about the domain of the variables
  • Coding sheet

Example from Skocpol

Ask a correct question

  • "What was the effect of cause X?" \(\checkmark\)
  • "What cause Y?" or "Variance of the effect of X?" \(\times\)

Toolbox of case study

Least-likely case

  • If the theory can make it here, it can make it anywhere.

  • E.g.: Evangelista(1999)
    • Target: Influence of transnational actor
    • Theory: Transnational actor can affect international relations
    • Case: U.S. vs. USSR
      • Scientists' contact affect the course of U.S. and Soviet defense and arm control policies.

Most similiar systems

  • Control similarity, focus on differences.

  • E.g.: Ray(1995)
    • Target: Interstate conflicts
    • Theory: Democratic peace
    • Case: UK-France Fashoda Crisis vs. Spanish-American War
      • Control for confounders (regression effects, mortality, selection bias) and same year
      • Explanatory: regime

Deviant Cases

  • Cases that do not conform to the predictions made by the theory or theories under investigation.

  • E.g.: Elman(1997)
    • Theory: Democratic peace
    • Case: Finland vs. UK in the Continuation War
      • Finland: Legislature does not balance president
    • Conclusion: decentralized vs. centralized democracies

Process tracing

  • Explicit attention to and process tracing on alternative explanations
  • Sustained focus on the question of "what else must be true" of the process
  • A wide variety of sources